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Functional effects of replacing human α‐ and β‐globins with their embryonic globin homologues in defined haemoglobin heterotetramers
Author(s) -
He Zhenning,
Lian Lurong,
Asakura Toshio,
Russell J. Eric
Publication year - 2000
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1046/j.1365-2141.2000.02065.x
Subject(s) - globin , biology , bohr effect , embryonic stem cell , microbiology and biotechnology , hemoglobin , in vitro , alpha globulin , beta (programming language) , biochemistry , gene , computer science , oxygen–haemoglobin dissociation curve , programming language
Embryonic‐ and adult‐stage globin subunits assemble into haemoglobin (Hb) heterotetramers that are expressed at low levels throughout human intrauterine development. These haemoglobins differ from adult Hb A (α 2 β 2 ) by the substitution of embryonic ζ for adult α globin (Hb ζ 2 β 2 ), or embryonic ε for adult β globin (Hb α 2 ε 2 ). Several key physiological properties of these ‘semiembryonic’ haemoglobins remain undefined, as ethical and methodological considerations have limited their availability from both human sources and conventional expression systems. The current study attempts to estimate how the physiological properties of semiembryonic and adult haemoglobins may differ, by determining whether the O 2 ‐binding characteristics of hybrid human/mouse haemoglobins change when human α‐ or β‐globin subunits are replaced by human embryonic ζ‐ or ε‐globin subunits respectively. Each of the four human globins is expressed in transgenic mice that are nullizygous for either the endogenous mouse α‐ or β‐globin genes, resulting in the high‐level expression of haemoglobins that can be studied either in situ in intact erythrocytes or in vitro . We showed that the exchange of human ζ‐globin for human α‐globin chains increased haemoglobin O 2 affinity, both in the presence and in the absence of 2,3‐bisphosphoglycerate (2,3‐BPG), and reduced the pH‐dependent shift in its oxygen equilibrium curve (Bohr effect). By comparison, hybrid haemoglobins containing either human ε‐globin or human β‐globin exhibited nearly identical O 2 ‐binding properties, both in situ and in vitro , regardless of 2,3‐BPG levels or ambient pH. Neither the ζ‐for‐α nor the ε‐for‐β substitutions substantially altered binding affinity for 2,3‐BPG or cooperativity between globin subunits. These studies suggest that semiembryonic haemoglobins that assemble entirely from human subunits may exhibit properties that are similar to those of human Hb A.